Adding MS-Word-like comments in LaTeX

Since LaTeX is a text format, if you want to show someone the differences in a way that they can use them (and cherry pick from them) use the standard diff tool (e.g., diff -u orig.tex new.tex > docdiffs). This is the best way to annotate something like LaTeX documents, and can be easily used by anyone involved in the production of a document from LaTeX sources. You can then use standard LaTeX comments in your patch to explain the changes, and they can be very easily integrated. If the document lives in a version control system of some sort, just use the VCS to generate a patch file that can be reviewed.

I have used changes.sty, which gives basic change colouring:

\added{new text}
\deleted{old text}
\replaced{new text}{old text}

All of these take an optional parameter with the initials of the author who did this change. This results in different colours used, and these initials are displayed superscripted after the changed text.

\replaced[MI]{new text}{old text}

You can hide the change marks by giving the option final to the changes package.

This is very basic, and comments are not supported, but it might help.

todonotes is another package that makes nice looking callouts. You can see a number of examples in the documentation.